This is on a '165 computer, 1989 vette, 6E ARAP based tune.

I've been fighting this for over a year now. New maf and old maf. Can't run closed loop tuning with my cam, can't kick the cam surge and have too much overlap at idle and light throttle. So, open loop tuning, here is the problem:

Full open loop, tune will be dialed in right where I want it at part throttle (mid 13's AFR on the wideband most of the time, which is what it seems to like). I'll shut the car off after about a 20 minute drive. Start it back up 2 minutes later and, just like flipping a light switch, it will be 2 or 2.5 points leaner (like mid 15's) on the wideband prettymuch everywhere, except WOT. WOT is still fine. I think because at WOT the MAF is maxed at 255 anyway and I fuel from there on up with the PE vs RPM table. I'm really thinking at this point the MAF is getting somewhat heat soaked and is not reading the gms/sec accurately. All else seems fine. No codes, nothing unordinary going on, fuel pressure holding great, nothing weird showing on the datalog, battery volts stay around 13.6, no weird steps in any coolant temp tables or anything.

I've changed everything. New Injectors, MAF, fuel cooler with fan, afpr, and tons of other stuff. I do add a little fuel at 198 degrees in the OL AFR%Chg vs Coolant temp because the coolant temps are up there when it happens, and that helped a little, but the heat soak on the maf (I am thinking) is independent of the coolant temp. Adding too much fuel there just makes it too rich at the higher normal operating temps, until I shut the car off and fire it back up minutes later, then it is lean.

Short of going to a SD conversion, how can I combat this? I'm tired of having a good tune, then end up lean. Tired of having a good tune, then do a WOT blast, and be way lean. A minute after a WOT blast is when it is the worst. Like on the lines of 16.5:1 (and can feel it cut out just a little at very light throttle) for a few minutes, then it creeps back down to the 14.5 range. Only after completely cooling off does it get back down to 13.5 or so, where it runs the best. After a long long drive the afr will slowly creep up, but it is most noticeable after shutting the car off for a couple minutes then starting it back up.

HELP! At this point the only thing I know left to try is to wrap the MAF in aluminum foil to see if it will help keep the heat from absorbing into it. Anyone have any other ideas of what I can do here?

 

Thanks for keeping me on the SD trail lol.

I hope their are lots more better replies than mine but;
I would not wrap the MAF, rather a heat shield between it and rising heat.

Contain exhaust heat with wrap or blankets.

And a goofy one, apply PC cooling tech to the MAF body.

 

I never heard of this happening nor have I ever experienced anything like this. I do recall seeing a slight difference in overall air fuel ratios in the summer vs winter air but nothing like you are describing. I'm not sure where to begin on advice, maybe try to heat insulate the MAF housing just to see what effect that has on it.

Makes me think something is wrong with the wiring and extra underhood engine heat could be effecting the voltage readouts to the ecm? Similar how heatsoaking a starter solenoid or the starter power wires causes hot restart problems. Doesnt get voltage due to resistance changes in the wire due to heat. Since you tried both new and old MAF's, I dont think its a MAF problem.

Where is your fresh air intake? This is a vette? Is it taking hot air off the radiator?

 

This is a 'vette, still has the stock air intake system. Since the MAF is just behind and above the radiator, one of my worries is that the fan is pulling all that hot air through the radiator and it is going right up across the MAF. Wasn't really thinking the air coming in would be hot because it takes it's air in out front of the radiator.

From searching on here it seems a few others have had the problem I'm having but nobody has ever posted a solution. I honestly don't know what else could cause this. I'm so tired of working out a tune, then shutting the car off, starting it right back up 1 minute later, and it is way lean. It is almost like the MAF resets itself after shut down and restart, and the part throttle tune is then lean till it gets shut down, cools off, then is restarted.

 

Closed loop is impossible for you to run? can you set the enable temp to something abit hotter than stock settings and ignore idle BLM's since overlap will lie to the ecm?

Just an idea to see if it works.

 

Wierd? never heard something like this before...Could you post 2 loggfiles where we can see the diffrences?

 

My log files will just show 128 INT and 128 BLM since I am running full open loop with the max and min int and blm set to 128.

Another thought I didn't add.....When I said I can shut the car off then start it right back up and it runs much leaner, I'm sure the MAF burnoff has activated when I shut the car off. I'm thinking that alone would make the MAF wires MUCH hotter, which is why it is the leanest right then, and does richen back up a little after driving just a little. I can kill the maf burnoff and set the number of missed burnoffs infinitely high before a check engine light comes on to cure this, but this is one more of the things that points me to the fact that when the maf (or maf wires) are hot, the tune is lean.

 

just curious about maf values/ BPW values and so on.

 

No matter what I tried to change, it always has a cam surge that feels like a cut out when I'm below about 2500 rpms. As soon as I go open loop and richen the mix to about 13.0 or 13.5 to 1, it runs great. I actually tried running closed loop, turning on highway mode fueling at around 45 mph, and setting the highway mode afr to 13.5:1. It actually worked fairly well. It was one way to run closed loop but be able to have a richer than 14.7:1 afr. But still wasn't as good as full open loop.

I actually might try wrapping the MAF in aluminum foil. Foil reflects like 95% of radiant heat and should work well since it won't be in direct contact with the heat source. Worth a try I guess.

 

That will help isolate burnoff & outside heat for diagnosis.

Mostly unrelated to the heat issue but,
You are running stoic @ 14.7 on today's pump fuel??
Fix that & give the o2 a corresponding target value.
Listen to the engine.
A 15.5:1 cruise is quite lean on the "premium" fuel I can get, that is crappy fuel.
I save the cruise development in separate bins & flash.
Mostly I run without.

There went your current VE tables, that never fails lol.
But you have to give the engine what it wants, and the ECM how to do it.

Anybody else compensate for what goes in the tank?
BTU's (fuel) first, then timing.

 

No, I am not running 14.7. My car cuts out, like a cam surge, when I run that lean at anything higher than about 64 LV8. I have it running at about 16.5 AFR around 40 LV8, which is decel only. At 64 LV8 I try to run around 14.0, everywhere else I target 13.0 to 13.5. That is what the engine seems to like. During AE I run about 12.5, during very heavy load very low rpm, like 3/4 throttle with the converter locked in OD, I shoot for about 12.0. PE mode, I float between 12.2 and 12.7. This is all on 93 octane with very little ethanol mix. Of course, with the issue I'm having, other than PE mode, I am a little richer than this when cooler and alot leaner than this when heat soaked.

Well, I can say I'm running 12.5 SCR and 9.2 DCR. I have to run 93 octane or it diesels back when I shut it off, especially if idling a little high or a little rich. I used to compensate for what went in the tank, if I ran 92 octane instead of BP 93, I'd drop in a chip with 2 degrees less timing. Fueling was about the same though, just leaned the idle a little and richened PE a hair. Found it easier to just fill up at the station close to my house all the time, they have 93 octane that seems good, so no more changing tunes due to different fuels.

I went out tonight and slid a heavy sock over my maf sensor and most of my intake ducting, and wrapped it in about 5 layers of aluminum foil. I duct taped the end seam. Very red neck! If it works I will get some aluminum foil insulating tape and use that. I drank 2 Michelobs before starting, 2 while working, then 2 with supper, so no test drive tonight. I'll keep you all posted on how it works out.

I can say that when I removed the MAF sensor the screen nearest the air cleaner fell out on it's own and the little plastic ring looked a little melted. I'm guessing it is getting VERY hot. A good long test drive or 2 will tell.

 

How hot are the underhood temps getting?

 

If anything, the intake ducting should show signs of melting as well. I would guess that the ring is probably a manufactures defect. Just a thought. Well dan0617, if you decide to let more air in the engine, visit this link to a do it yourself mod......
http://www.lewzworld.com/camaro/mods/maf.html

 

I'm not real sure. Feels hot enough to make the boogers drip right out of my nose when standing over it after a long drive on a hot day. I'll bring a digital heat gun home from work for a few days and check it out.

I had my last MAF totally descreened. This one now has the screen on the inlet side of the MAF removed. I might remove the other one and the fins, but want to try this one step at a time. If I am having this much trouble keeping the MAF cool then the fins might be helping me. If insulating and wrapping the MAF in aluminum foil deters enough heat to solve my problem, I will try removing the fins and see if it gets better or worse.

 

Properly functioning MAF should compensate fully for air temps and should have little or no deviation as air temps change. This is due to the fact that the heated element is maintained at a constant delta T with respect to the ambient air temp sensing element.

This sounds like a problem with the internal circuitry of the MAF. I would insulate the exhaust primaries to contain the heat, and replace the MAF.

Do you have your airdam in place and what not?

I would also NOT remove teh heatsink fins from the MAF. That will just make things worse.

 

IT MAY BE FIXED!

Went on about a 30 minute drive highway, then about 15 minutes of stop and go in town driving. Outside temp is about 88 degrees. Coolant temp got up to about 210. Shut car off. Started it back up, AFR's were still the same. Went into chiropractor (first visit of my life, but my back is bad right now). Came out, started car up, AFR's still good. Got it hot in town driving again, actually got richer (had my OL AFR%chg vs coolant temp adding some fuel at 198 degrees and above. Came home, burnt a new chip with a few little changes and cut way down on the fueling from 198 degrees on up, went for another drive, and all seems fine. Popped the hood. Intake is so hot I can't hardly lay my hand on it.....but the air intake, wrapped in double sided aluminum bubble wrap and aluminum tape, is cool to the touch! The aluminum foiling really does reflect all the radiant heat coming off the fan from the radiator. I'll keep you all posted but insulating the maf in something with an aluminum foil surface may be the ticket to keeping a consistent tune with atmospheric temperature changes!

 

dan0617, sounds like your onto something. Gots me interested in your method of insulating the intake. Keep us posted on your progress.

 

I ended up buying bubble wrap that is aluminum foiled on both sides, and some aluminum tape. Bought both things at Lowe's. So far so good. I'm tweaking a few things in the tune. I ended up removing both screens and all but the bottom 2 fins from inside the maf, so my maf tables needed tweaked a little. Just got back from another drive and so far so good, no major jumps in AFR at part throttle like before.

 

Congrats, seems like your initial concerns of the MAF getting too hot and screwing up the tune was correct. Knock on wood, i hope i didnt speak too soon.

I never had a problem with my large tube MAF i made but that motor never got too hot. Never got above 210. I dont think a MAF could survive under the hood of my turbo setup now... soo hot.

 

I just wish that was my initial concern. I've spent hundreds of hours tuning and working on the car to find this problem.